U.S. patent application number 15/216149 was filed with the patent office on 2018-01-25 for apparatus and method to apply voltage to fuel cell stack from high voltage system for usage during diagnostic tests.
The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to JOSEPH BERG, KENNETH L. KAYE.
Application Number | 20180026463 15/216149 |
Document ID | / |
Family ID | 60890492 |
Filed Date | 2018-01-25 |
United States Patent
Application |
20180026463 |
Kind Code |
A1 |
BERG; JOSEPH ; et
al. |
January 25, 2018 |
APPARATUS AND METHOD TO APPLY VOLTAGE TO FUEL CELL STACK FROM HIGH
VOLTAGE SYSTEM FOR USAGE DURING DIAGNOSTIC TESTS
Abstract
A fuel cell charging system includes a fuel cell stack having a
first operating direct current (DC) voltage between fuel check
stack terminals, a high voltage system operating at a first DC
operating voltage different than and generally higher than the
first operating voltage of the fuel cell stack, a boost converter
in electrical connection with the fuel cell stack and the high
voltage system, and a stack charging component that applies a
second DC operating voltage, generally of lower value than that of
the first normal operating voltage, to the fuel cell stack. The
boost converter transfer electrical power from the fuel cell stack
to the high voltage system during fuel cell operation.
Characteristically, the second DC operating voltage applied to the
fuel cell stack terminals is typically lower in value than that of
the first DC operating voltage of both the fuel cell stack and the
HV electrical system and is stepped down from the first DC
operating voltage of the HV electrical system.
Inventors: |
BERG; JOSEPH; (WEST
BLOOMFIELD, MI) ; KAYE; KENNETH L.; (ROCHESTER HILLS,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
Detroit |
MI |
US |
|
|
Family ID: |
60890492 |
Appl. No.: |
15/216149 |
Filed: |
July 21, 2016 |
Current U.S.
Class: |
320/101 |
Current CPC
Class: |
H02J 7/00 20130101; Y02E
60/50 20130101; H02J 2300/30 20200101; H01M 8/04873 20130101; Y02T
90/40 20130101; H02M 3/158 20130101; H02J 2207/20 20200101; H02M
3/156 20130101; H01M 8/04992 20130101; H01M 8/04888 20130101; H01M
2250/20 20130101; H01M 8/0488 20130101; H01M 8/04082 20130101 |
International
Class: |
H02J 7/00 20060101
H02J007/00; H01M 8/04992 20060101 H01M008/04992; H02M 3/156
20060101 H02M003/156; H01M 8/04828 20060101 H01M008/04828 |
Claims
1. A fuel cell charging system comprising: a fuel cell stack having
a fuel cell stack voltage between fuel check stack terminals, the
fuel cell stack voltage being at a first voltage during normal fuel
cell operation; a high voltage electrical system operating at a
first DC operating voltage, the first DC operating voltage being
higher than the first voltage of the fuel cell stack; a boost
converter in electrical connection with the fuel cell stack and the
high voltage electrical system, the boost converter transferring
electrical power from the fuel cell stack to the high voltage
electrical system during fuel cell operation; a step down voltage
component that applies a second DC operating voltage to the fuel
cell stack, the second DC operating voltage being stepped down from
the first DC operating voltage of the high voltage electrical
system to a charging voltage that is lower than the first voltage
of the fuel cell stack during normal operation; and a FCS
controller that is operable to send control signals to the boost
converter and the step down voltage component.
2. The fuel cell charging system of claim 1 wherein the FCS
controller is operable to disable the boost converter when the
second DC operating voltage is applied to the fuel cell stack.
3. The fuel cell charging system of claim 1 further comprising a
stack discharge circuit that when enabled reduces the voltage of
the fuel cell stack through resistive energy discharge
4. The fuel cell charging system of claim 3 wherein the FCS
controller determines if the fuel cell stack voltage is within
predetermined voltage window having an upper voltage limit and a
lower voltage limit.
5. The fuel cell charging system of claim 4 wherein the FCS
controller is operable to send a control signal to enable the stack
discharge circuit when the fuel cell stack voltage is above the
upper voltage limit.
6. The fuel cell charging system of claim 5 wherein the FCS
controller is operable to send a control signal to disable the
stack discharge circuit when the fuel cell stack voltage is below
the upper voltage limit.
7. The fuel cell charging system of claim 4 wherein the upper
voltage limit is from 25 to 50 volts and the lower voltage limit is
from 15 to 25 volts.
8. The fuel cell charging system of claim 4 wherein the
predetermined voltage window is from 10 to 30 volts.
9. The fuel cell charging system of claim 4 wherein the FCS
controller is operable to perform diagnostic test when the fuel
cell stack voltage is within the predetermined voltage window.
10. A fuel cell charging system comprising: a fuel cell stack
having a fuel cell stack voltage between fuel cell stack terminals,
the fuel cell stack voltage being at a first voltage during normal
fuel cell operation; a high voltage electrical system operating at
a first DC operating voltage, the first DC operating voltage being
higher than the first voltage of the fuel cell stack; a boost
converter in electrical connection with the fuel cell stack and the
high voltage electrical system, the boost converter transferring
electrical power from the fuel cell stack to the high electrical
voltage system during fuel normal cell operation; a buck converter
that applies a second DC operating voltage to the fuel cell stack,
the second DC operating voltage being stepped down from the first
DC operating voltage of the high voltage electrical system to a
voltage below the first voltage during normal fuel cell operation;
and an FCS controller that is operable to send control signals to
the boost converter and the buck converter.
11. The fuel cell charging system of claim 10 wherein the FCS
controller is operable to disable the boost converter when the
second DC operating voltage is applied to the fuel cell stack.
12. The fuel cell charging system of claim 10 further comprising a
stack discharge circuit that when enabled reduces the voltage of
the fuel cell stack through resistive energy discharge.
13. The fuel cell charging system of claim 10 wherein the FCS
controller determines if the fuel cell stack voltage is within a
predetermined voltage window having an upper voltage limit and a
lower voltage limit.
14. The fuel cell charging system of claim 13 wherein the upper
voltage limit is from 25 to 50 volts and the lower voltage limit is
from 15 to 25 volts.
15. The fuel cell charging system of claim 13 wherein the
predetermined voltage window is from 10 to 30 volts.
16. The fuel cell charging system of claim 13 wherein the FCS
controller is operable to the buck converter to regulate the
voltage of the fuel cell stack
17. The fuel cell charging system of claim 13 wherein the FCS
controller is operable to perform diagnostic test when the fuel
cell stack voltage is within the predetermined voltage window.
Description
TECHNICAL FIELD
[0001] In a least one aspect, the present invention is related to
systems and methods for charging a fuel cell stack to a voltage
that is useful for performing diagnostic tests.
BACKGROUND
[0002] Fuel cell stacks are used as an electrical power source in
many applications. In particular, fuel cell stacks are proposed for
use in automobiles to replace internal combustion engines. In
typical applications, fuel cell stacks are provided in arrays of
many individual fuel cells in order to provide high levels of
electrical power. The complexity of fuel cell stacks which can have
several hundred individual fuel cells necessitates that strategies
and conditions for efficient testing be developed.
[0003] Accordingly, there is a need for fuel cell charging systems
that can maintain a fuel cell stack at a voltage that is useful for
performing a certain subset of diagnostic tests.
SUMMARY
[0004] The present invention solves one or more problems of the
prior art, by providing in at least one embodiment, a fuel cell
charging system that transfers electrical power from a high voltage
electrical system to a fuel cell stack. The fuel cell charging
system includes a fuel cell stack having a first direct current
(DC) voltage between fuel check stack terminals, a high voltage
system operating at a first DC operating voltage, different than,
and generally higher than that of the first voltage of the fuel
cell stack, a boost converter in electrical connection with the
fuel cell stack and the high voltage system, and a step down
voltage component that applies a second DC operating voltage to the
fuel cell stack. The fuel cell stack voltage is at (i.e., outputs)
the first voltage during normal fuel cell operation. The boost
converter transfers electrical power from the fuel cell stack to
the high voltage system during normal fuel cell operation.
Characteristically, the second DC operating voltage is stepped down
from the first DC operating voltage of the high voltage electrical
system to a fuel cell stack charging voltage that is lower than the
first voltage of the fuel cell stack. The fuel cell charging system
also includes an FCS (fuel cell system) controller that is operable
to send control signals to the boost converter and the step down
voltage component. The present embodiment uses a switch/resistor
combination across a standard boost converter in conjunction with
standard stack discharge circuitry already present in the system to
apply and regulate the value of voltage applied to the terminals of
the stack for diagnostic algorithms. Advantageously, the fuel call
charging system allows implementation of a stack charging function
with potential reduced cost from an implementation that requires an
additional insulated-gate bipolar transistor (IGBT) module in a
boost converter to create a buck converter to control voltage at
stack terminals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a schematic illustration of a fuel cell charging
system that utilizes a switch and transistor for charging a fuel
cell stack;
[0006] FIG. 2 is a schematic illustration of a fuel cell charging
system that utilizes a buck converter for charging a fuel cell
stack; and
[0007] FIG. 3 is a flowchart illustrating the operation of the fuel
cell charging systems of FIG. 1.
DETAILED DESCRIPTION
[0008] Reference will now be made in detail to presently preferred
compositions, embodiments and methods of the present invention,
which constitute the best modes of practicing the invention
presently known to the inventors. The Figures are not necessarily
to scale. However, it is to be understood that the disclosed
embodiments are merely exemplary of the invention that may be
embodied in various and alternative forms. Therefore, specific
details disclosed herein are not to be interpreted as limiting, but
merely as a representative basis for any aspect of the invention
and/or as a representative basis for teaching one skilled in the
art to variously employ the present invention.
[0009] Except in the examples, or where otherwise expressly
indicated, all numerical quantities in this description indicating
amounts of material or conditions of reaction and/or use are to be
understood as modified by the word "about" in describing the
broadest scope of the invention. Practice within the numerical
limits stated is generally preferred. Also, unless expressly stated
to the contrary: the first definition of an acronym or other
abbreviation applies to all subsequent uses herein of the same
abbreviation and applies mutatis mutandis to normal grammatical
variations of the initially defined abbreviation; and, unless
expressly stated to the contrary, measurement of a property is
determined by the same technique as previously or later referenced
for the same property.
[0010] It is also to be understood that this invention is not
limited to the specific embodiments and methods described below, as
specific components and/or conditions may, of course, vary.
Furthermore, the terminology used herein is used only for the
purpose of describing particular embodiments of the present
invention and is not intended to be limiting in any way.
[0011] It must also be noted that, as used in the specification and
the appended claims, the singular form "a," "an," and "the"
comprise plural referents unless the context clearly indicates
otherwise. For example, reference to a component in the singular is
intended to comprise a plurality of components.
[0012] The term "comprising" is synonymous with "including,"
"having," "containing," or "characterized by." These terms are
inclusive and open-ended and do not exclude additional, unrecited
elements or method steps.
[0013] The phrase "consisting of" excludes any element, step, or
ingredient not specified in the claim. When this phrase appears in
a clause of the body of a claim, rather than immediately following
the preamble, it limits only the element set forth in that clause;
other elements are not excluded from the claim as a whole.
[0014] The phrase "consisting essentially of" limits the scope of a
claim to the specified materials or steps, plus those that do not
materially affect the basic and novel characteristic(s) of the
claimed subject matter.
[0015] The terms "comprising", "consisting of", and "consisting
essentially of" can be alternatively used. Where one of these three
terms is used, the presently disclosed and claimed subject matter
can include the use of either of the other two terms.
[0016] With reference to FIG. 1, a schematic illustration of a
system to apply a voltage to a fuel cell stack from a high voltage
is provided. Fuel cell charging system 10 includes fuel cell stack
12 which includes a plurality of individual fuel cells. Fuel cell
stack 12 is characterized by a fuel cell stack voltage between
voltage terminals 14, 16. During normal fuel cell operation, the
fuel cell stack voltage is at a first voltage that is outputted to
a load. In typical automotive applications, fuel cell stack
includes from 20 to 350 (or more) individual fuel cells each
operating at a voltage from about 0.6 to 1.22 volts per fuel cell.
Therefore, the fuel cell stack voltage can be between 12 to 430
volts. Boost converter 20 is in electrical connection with fuel
cell stack 12 and high voltage system 22. High voltage system 22
operates at a first DC operating voltage. The first DC operating
voltage of high voltage system 22 is higher than the first voltage
which is outputted by the fuel cell stack 12. Boost converter 20
transfers electrical power from fuel cell stack 12 to the high
voltage system 22 during fuel cell operation. In a refinement, high
voltage system 22 provides voltage to a vehicle in which fuel cell
charging system 10 and fuel cell stack 12 is incorporated.
Typically high voltage system 22 includes high voltage battery 24.
Stack charging component 26 applies a second DC operating voltage
in a time controlled manner to the fuel cell stack 12 between
voltage output terminals 14, 16. In the variation depicted in FIG.
1, stack charging component 26 utilizes resistor 28 and switch 30
to accomplish reducing the voltage applied to terminals 14 and 16
of fuel cell stack 12. Characteristically, the second DC operating
voltage is stepped down from the first DC operating voltage high
voltage system 22 to a charging voltage that is lower than the
first voltage of fuel cell stack 12 outputted during normal
operation.
[0017] Fuel cell system 10 also includes stack discharge circuit 32
for reducing the voltage of the fuel cell stack through resistive
energy discharge during other modes of operation. For this purpose,
stack discharge circuit 32 includes resistor 34 and switch 36.
Switch 30 allows for the connection of the circuit between the fuel
cell stack and the high voltage system. Resistor 28 is sized to
limit the inrush of current to the fuel cell stack and to control
the rate of voltage rise across terminals 14, 16. Stack discharge
circuit 32 is used initially to bring down the voltage within a
predetermined voltage window having an upper voltage limit and a
lower voltage limit. In a refinement, the predetermined voltage
window is from 10 to 30 volts. In a further refinement, the upper
voltage limit is from 25 to 50 volts and the lower voltage limit is
from 15 to 25 volts. Stack charging component 26 is then used bring
the voltage up if the level falls to low.
[0018] Still referring to FIG. 1, boost converter 20 is typically a
standard boost used in fuel cell systems to provide electrical
power from a fuel cell stack to a high voltage system. Boost
converter 20 include microprocessor 40 which controls transistor 42
via gate controller 44. Boost converter accomplishes the power
transfer to the high voltage system via switch 42, inductor 48,
diode 50, diode 52, and capacitor 54. The function of a boost
converter is to increase the input voltage to a higher output
level. This is achieved through Pulse Width Modulation control of
transistor 42. During time that transistor 42 is on (TON) the
current from the Fuel Cell Stack System flows through inductor 48
and transistor 42. The energy returns to fuel cell stack through
wire 56 thereby creating energy stored in inductor 48 as well as a
voltage rise across inductor 48. When transistor 42 transitions off
the energy stored in inductor 48 causes the current to flow to the
output load (i.e., high voltage system 22) and the voltage at the
output of boost converter 20 is the sum of the voltage across the
inductor and the stack voltage, which is higher than the initial
input voltage from the fuel cell stack. In a normal fuel cell
application, the boost converter microprocessor 40 controls the
stack average output current (boost input current) by regulation of
the duty cycle.
[0019] Fuel cell system 10 also includes FCS controller 60. FCS
controller 60 is used to control boost converter 20 and stack
discharge circuitry 32. In this regard, the term "operable" means
that FCS controller 60 either issues control signals and/or
instructions to a device being controlled to perform a certain
function or to return a measurement from a sensor. For example,
during the operation of FCS controller 60, FCS controller issues
control signals to microprocessor 40 of boost converter 20. These
functions for stack FCS controller 60 are standard for many prior
art systems. However, in the present embodiment FCS controller 60
also controls stack charging component 26 by enabling and disabling
charging of fuel cell stack 12 from high voltage system 22. In
particular, FCS controller 60 is operable to disable the boost
converter when the second DC operating voltage is applied to fuel
cell stack 12 during diagnostic mode operation. FCS controller 60
determines if the fuel cell stack voltage is within the
predetermined voltage window. Therefore, FCS controller 60 is
operable to send a control signal to enable the stack discharge
circuit when the fuel cell stack voltage is above the upper voltage
limit and to send a control signal to disable the stack discharge
circuit when the fuel cell stack voltage is below the upper voltage
limit. Advantageously, FCS controller 60 is operable to perform
diagnostic test when the fuel cell stack voltage is within the
predetermined voltage window.
[0020] With reference to FIG. 2, a schematic illustration of a
different system to apply a voltage to a fuel cell stack from a
high voltage is provided. Fuel cell charging system 10' includes
fuel cell stack 12 which includes a plurality of individual fuel
cells. Fuel cell stack 12 has a fuel cell stack voltage between
voltage terminals 14, 16. During normal fuel cell operation, the
fuel cell stack voltage is a first voltage that is outputted. Boost
converter 20 is in electrical connection with fuel cell stack 12
and high voltage system 22. High voltage system 22 operates at a
first DC operating voltage. The first DC operating voltage is
higher than the first voltage of the voltage seen at terminals 14
and 16 of fuel cell stack 12. Boost converter 20 transfers
electrical power from fuel cell stack 12 to the high voltage system
22 during fuel cell operation. In a refinement, high voltage system
22 provides voltage to a vehicle in which fuel cell charging system
10 and fuel cell stack 12 is incorporated. Typically high voltage
system 22 includes high voltage battery 24. Step down voltage
component 26' applies a second DC operating voltage to the fuel
cell stack 12 between voltage output terminals 14, 16. In the
variation depicted in FIG. 2, step down voltage component 26' is a
buck converter. In a refinement, microprocessor 40 is used to
control both boost convert 20 and the buck converter.
Characteristically, the second DC operating voltage is stepped down
from the first DC operating voltage to a charging voltage that is
lower than the first voltage by the buck converter. Fuel cell
system 10' also includes stack discharge circuit 32 for discharging
the fuel cell stack when necessary. For this purpose, includes
stack discharge circuit 32 includes resistor 34 and switch 36. In
this variation using a buck converter, stack discharge circuit 32
may or may not be disabled. The details of boost converter 20 and
FCS controller 60 are set forth above in the description of FIG. 1.
As set forth above, FCS controller 60 controls the buck converter
by enabling and disabling charging of fuel cell stack 12 from high
voltage system 22. In particular, FCS controller 60 is operable to
disable the boost converter when the second DC operating voltage is
applied to fuel cell stack 12. FCS controller 60 determines if the
fuel cell stack voltage is within the predetermined voltage window.
Advantageously, FCS controller 60 is operable to perform diagnostic
test when the fuel cell stack voltage is within the predetermined
voltage window.
[0021] With reference to FIGS. 1 and 3, the operation of the fuel
cell charging systems is described. FIG. 3 is a flowchart
illustrating the protocol followed by the systems of FIG. 1 for
charging the fuel cell stack is provided. Each of the steps set
forth in FIG. 3 can be performed by FCS controller 60 by sending
appropriate control signals or manually by a user. In block 100,
the fuel cell stack charging mode is enabled. This enabling
typically occurs by a user operating FCS controller 60, but can in
certain operating modes occur as an automatic function. In block
102, the set points for the stack charging mode are determined and
applied. The operations in block 102 can be performed by a user
and/or FCS controller 60. These set points include the upper and
lower limits of a window for the voltage that is to be applied to
fuel cell stack 12. In block 104, FCS controller 60 enables stack
discharge circuit 32 to bring down stack voltage.
[0022] In block 106, FCS controller 60 determines whether or not
the stack voltage below is below the window upper limit. If the
stack voltage is below the window upper limit, FCS controller 60
disables stack discharge voltage circuit 32 (block 108). If the
stack voltage is below the window upper limit, FCS controller 60
continues to keep stack discharge voltage circuit 32 enabled until
the stack voltage is below the upper window limit. When the stack
voltage is below the upper window limit, FCS controller 60
determines if a request to exit stack charging mode has been made
(block 110). If a request is made to exit stack charging mode, FCS
controller 60 resets system set points for normal fuel cell
operation (block 112) and then causes the system to exit stack
charging mode (block 114). If such a request is not made, FCS
controller 60 determines if the stack voltage is below the lower
limit of the voltage window. If the stack voltage is not below the
lower limit, the system returns to the operations of block 110
which can include conduction the diagnostic tests. If the stack
voltage is below the lower window limit, the system proceeds to
execute the operations of block 116 in which the FCS controller 60
sends a control signal to stack charging component 26 to charge
fuel cell stack 12. If the stack voltage is below the lower window
limit, the system returns the operations of block 116 in which
stack charging component 26 continues to charge fuel cell stack 12.
If the stack voltage is not below the lower window limit, FCS
controller 60 sends a control signal to disable switch 30 of stack
charging component 26. The system then cycles back to perform the
operations of block 106 in which FCS controller 60 queries to
determine is the stack voltage is below the window upper limit.
While exemplary embodiments are described above, it is not intended
that these embodiments describe all possible forms of the
invention. Rather, the words used in the specification are words of
description rather than limitation, and it is understood that
various changes may be made without departing from the spirit and
scope of the invention. Additionally, the features of various
implementing embodiments may be combined to form further
embodiments of the invention.
* * * * *